One of the largest onshore process complex receives and processes sour gas, condensate and crude from the offshore fields. Due to ageing of existing fields and production from new fields with different reservoir fluid characteristic, the composition of gas varies considerably with respect to the composition at inception, especially with reference to C3+ components. Opportunities were explored for enhancement of recovery of heavier components for value addition from the available gas in the existing scenario.

Presently, irrespective of their richness, with reference to C3+ components, all the gas streams such as slug catchers gas (molecular weight around 20.65 to 21.02), off gases from stabilization units and condensate fractionation units (molecular weight around 25.11 to 27.12) are combined and are routed for gas processing with the resultant combined gas molecular weight of around 21.01.

To evaluate the effect of processing of only rich gas streams in an exclusive gas sweetening unit and then further processing at a LPG unit was conceptualized by means of an integrated simulation model developed in Aspen Hysys process simulator.

Simulation model was calibrated and matched with the existing field operating parameters. All the rich gas streams such as one of the rich trunk line gas (molecular weight around 21.02), off gases from stabilization (molecular weight around 25.11) and fractionation units (molecular weight around 27.12) were segregated and processed in an exclusive gas processing train. Study established that the envisaged resultant combined rich gas molecular weight will be around 22.01. An analysis of preferentially processing of rich gas in one of the LPG unit with reference to production of LPG & Naphtha was carried out. Study examined the adequacy check of existing equipments such as pressure vessel, pumps, columns, exchangers, pipelines and their control valves. Study reviewed the modification requirements and also indicated the optimum parameters such as temperature, pressure to be followed in various processing units for effective recovery of heavier components from the gas.

The study established that preferential processing of rich gas in one exclusive train of gas sweetening unit and then in turbo expander-propane based LPG extraction unit resulted in enhancement of around 17% increase in LPG production and around 2.6% increase in Naphtha production from the existing production level of the complex.

Presently no provision exists to preferentially process the rich gas stream. Study elaborates the ways and means to be adopted for preferential processing of rich gas in the complicated gas processing complex considering flow, pressure, and temperature parameters including safety & flexibility of the plant operations by simple modifications.

This case study highlights the hidden opportunities in an existing processing complex to enhance the product yield and to gain additional revenue generation.

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